The use of topical or dermal anesthetics has long been utilized in the practice of medicine. Topical anesthetics are commonly administered prior to procedures such as injections, biopsies, the application of laser energy for cutaneous procedures such as removal of hair, tattoos, telengectasias, etc., minor superficial surgeries, and the like.
One particular topical anesthetic utilized to suppress or eliminate pain during such procedures is known by the trade name EMLA®. This product is known to be effective as a topical anesthetic; however, EMLA® has a very long onset time, which is the time between administration of the topical anesthetic and the commencement of the anesthetic effect. It must also be covered with an occlusive dressing to enhance penetration. The onset time for EMLA® can range from 45 to 90 minutes and, in some instances, can take even longer. The variability in length of onset time leads to delays in the commencement of medical procedures and, because of the very wide variation in onset time, can lead to the premature commencement of procedures, thereby inflicting unnecessary pain on the patient.
Several topical anesthetic formulations have been extensively used by the medical field to obtain local anesthesia. These products are known to be effective as topical anesthetics; however, they typically have long onset times, which is the time between the administration of the topical anesthetic and the commencement of the anesthetic effect. They must also be covered with an occlusive dressing to enhance penetration. Also, the onset of action for these available topical anesthetics varies over a range of time, for example from 45 to 90 minutes. This variability in length of onset time leads to delays in the commencement of medical procedures and, because of the very wide variation in onset time, can lead to the premature commencement of procedures, thereby inflicting unnecessary pain on the patient. These current methods have used more viscous semi-liquid carriers such as creams, ointments or gels which can be quite messy to work with, which adds another inconvenience to the user. For example, they must be cleaned off the injection site before injecting.
Accordingly, it would be advantageous and desirable to develop a topical anesthetic formulation which has a shorter onset time, which has less variability in the onset time, does not require occlusion, is easier to apply with less mess and which is amenable to use for cutaneous laser procedures such as hair removal and skin resurfacing, as well as for use before giving injections, starting IVs, drawing blood, biopsies and minor superficial surgeries. Such a formulation will have a potent clinical use with a more rapid onset of action.
The ideal vehicle for such a formulation would enhance the percutaneous penetration of the active ingredient, allowing for a fast onset of action. At the same time, the active ingredient must not penetrate so effectively through the skin as to be rapidly lost to the systemic circulatory systems. Thus, the ideal vehicle would also enhance the skin's ability to retain the pharmacologically active ingredient or, in other words, to increase skin residence times.